European chafer (Rhizotrogus majalis) beetle may be lurking in your lawn
This insect spends most of its life cycle as a grub (immature form) feeding on grass roots. Higher numbers of feeding grubs could result in your lawn turning brown, and you may even be able to lift up the grass easily due to a lack of roots. Natural predation of these grubs by skunks, raccoons or birds can make the lawn damage look even more severe.
There is a lot of information on this turf pest already documented back East, but timing of emergence and the length of its actual biological life cycle on the West Coast is still to be determined. This is important to know when trying to develop control measures for the future.
The European chafer has one life cycle per year and its interesting mating ritual begins in early summer with the small (1.25 cm) brown adult beetles gathering on the ground, usually after sunset. Within a few hours, masses of them will launch their mating flight to tall, vertical structures, such as trees, light poles or chimneys. In the darkness they may sound like a swarm of bees.
The adult beetle rarely produces any damage. After mating, female beetles re-enter the ground to lay their eggs, which will hatch into grubs by midsummer. With the onset of colder temperatures, the grub moves deeper into the soil, but when the ground warms up, it will migrate close to the surface to feed on the roots of your lawn.
Tips for controlling the European chafer beetle
Any control measure will have various limitations, but the following tips may be helpful:
• Dig out a square foot of sod and look at the patch removed to determine if grubs are present and currently doing damage. If they are, then control measures would be warranted.
• Maintain a high level of care to the lawn (e.g., watering, feeding, top-dressing, etc.) to help it more easily tolerate a population of grubs.
• Skunks, raccoons or birds can be easily attracted to grub populations in the ground. To minimize the turf damage these creatures cause, consider discouraging them from your lawn with the addition of fencing or the presence of a dog. Some people have tried keeping a light on outside at night to discourage visits by nocturnal pests like skunks and raccoons.
• You may want to try an environmentally friendly nematode soil drench. Soil temperature and moisture, and nematode species are a few factors that can affect its successful use. The nematodes are available at garden centres in late June to early July and are easy to use. It is as simple as watering the area with the biological treatment. One treatment will cover roughly 100 square m (1100 sq. ft.).
• Any soil being moved from one location to another should be checked carefully for grubs. Remember, though, that the grubs and eggs may be difficult to see in their early stages, so it is best to avoid moving soil if possible. Take note especially when transplanting plants, and be cautious when borrowing tools or any gardening supplies.
• Consider replacing the lawn with perennial ground covers. Vinca minor (periwinkle, zone 4), Thymus pseudolanuginosis (woolly thyme) or Chamaemelum nobile (Roman chamomile) are good choices.
Conway Lum is a horticulturist at Mandeville Garden Centre in Burnaby. Questions can be emailed to him at clumATcanadawideDOTcom.